The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Deposition of tungsten-containing film using chemical vapor deposition (CVD) is an integral part of many semiconductor fabrication processes. Tungsten-containing film may be used for horizontal interconnects, vias between adjacent metal layers, contacts between a first metal layer and the devices on the silicon substrate, and high aspect ratio features. During deposition, a substrate is heated to a process temperature in a deposition chamber. A liner/barrier layer made of titanium or titanium nitride (TiN) is deposited. Thereafter, the tungsten-containing film (the bulk layer) is deposited on the liner/barrier layer.
Depositing tungsten-containing film into high aspect ratio features may cause formation of seams inside the features. The seams may lead to high resistance, contamination and loss of filled materials. In other words, the seams degrade performance of integrated circuits. For example, a seam may extend close to a field region after the filling process and then open during chemical-mechanical planarization.
Referring now to FIGS. 1A-1D, an example of a process according to the prior art for filling a recessed feature with tungsten-containing film is shown. In FIG. 1A, a substrate 100 includes a recessed feature 104 such as a contact or via hole to be filled with W. In FIG. 1B, a liner/barrier layer 108 is deposited. The liner/barrier layer 108 may be made of titanium (Ti) or titanium nitride (TiN). The liner/barrier layer 108 typically creates an overhang 110 or pinch point near an opening of the recessed feature 104. A tungsten-containing film 112 is then deposited over the liner/barrier layer 108 using CVD deposition.
Filling features with tungsten-containing film may cause formation of seams inside the filled features. A seam can form when a layer that is being deposited on the side walls of the feature thickens to the point that it seals off a void space below the sealing point (also referred to as a pinch point). The pinch point prevents precursors and/or other reactants from entering the void space, which remains unfilled. The void space or seam is also sometimes referred to as a keyhole. In FIG. 1C, a keyhole 114 remains after deposition. In FIG. 10, chemical mechanical planarization (CMP) opens the keyhole 114.
In FIGS. 2A-2D, another example of a process according to the prior art for filling a recessed feature with a tungsten-containing film is shown. In FIG. 2A, a substrate 130 includes a recessed feature 134 such as a contact or via hole. A liner/barrier layer 138 is deposited. The liner/barrier may be made of Ti/TiN and may create an overhang 140. A W layer 142 is then deposited over the liner/barrier layer 138 using partial W CVD deposition. In FIG. 2B, an etch back step is performed with a fluorine species. Repeated deposition-etch cycles may be performed to reduce a keyhole 144 and seam in the W fill. In FIG. 2D, a CMP step may be used to open the keyhole 144.
The approach of FIGS. 2A-2D involves a partial fill in a first deposition step, which leaves the via open during a subsequent etch step. The subsequent etch step targeted at W removal in the field and overhang tends to have an unwanted side effect. The subsequent etch step also removes the W inside the via. A subsequent deposition step regrows W at the same rate inside the via and at the overhang, which results in the same keyhole void.